1. Field of the Invention
The present invention relates to control of a vehicular automatic transmission equipped with a manual shift function and to a field of shifting technique in vehicles.
2. Description of the Related Art
Vehicular equipped with an automatic transmission that can be operated in an automatic shift mode in which the shift stages are shifted automatically according to the travel state, and a manual shift mode in which the shift stages are switched by a manual operation performed by a driver, have found practical use in recent years. When the manual shift mode is executed, the present shift stage is displayed by an indicator on an instrument panel. Further, the manual shift mode includes a manual mode executed by selecting, for example, a special shift range called “M range” by operating a shift lever, and a direct mode temporarily executed by operating an upshift switch or a downshift switch provided at a steering wheel.
Continuously variable transmissions (CVT) equipped with an automatic shift mode, in which the shift ratio is changed automatically according to the travel state, and a manual shift mode, in which the shift ratio is switched in a stepwise manner by a manual operation performed by the driver, have also been known. In a vehicle equipped with a continuously variable transmission of this kind, a plurality of shift stages are set in advance for the manual shift mode, and when the manual shift mode is executed, the present shift stage is displayed at the indicator.
For the sake of convenience of explanation, the term “automatic transmission” used hereinbelow will be assumed to include not only a multistep automatic transmission equipped with a mechanism for switching the shift ratio in a stepwise manner, but also a stepless automatic transmission equipped with a mechanism that continuously changes the shift ratio.
In the automatic transmission provided with such a manual shift function, a shift stage is basically selected by a manual operation performed by the driver when the manual shift mode is executed. However, in order to protect the engine, a shift stage is sometimes automatically shifted depending on the travel state even in the manual shift mode. More specifically, for example, an automatic upshift is executed when the engine revolution speed exceeds an upper limit value, and an automatic downshift is executed when the vehicle speed decreases and the engine revolution speed becomes lower than the lower limit value. The control by which upshifting and downshifting are thus automatically executed in the manual shift mode is referred to as “automatic shift control”.
However, since shifting unintended by the driver is executed in the automatic shift control, the driver sometimes performs a shift operation while disregarding the execution of such shifting as the automatic shift control is performed, and in such cases, two-stage shifting is performed contrary to the driver's intention. For example, when the upshifting is automatically executed following the increase in the engine revolution speed as the vehicle travels at the first speed in the manual shift mode, where the driver upshifts to a second speed in the course of such control, the upshifting is performed to a third speed contrary to the driver's intention, and the driver is given an uncomfortable feeling, namely, the acceleration force expected by the driver is not obtained.
To resolve this problem, Japanese Patent Application Publication No. H10-89466 discloses the technique by which when upshifting is automatically executed in the manual shift mode, the execution of upshifting by the driver's operation is prohibited till a predetermined time elapses. With the technique disclosed in Japanese Patent Application Publication No. H10-89466, the execution of the two-stage upshifting contrary to the driver's intention in the manual shift mode can be prohibited.
However, with the technique disclosed in Japanese Patent Application Publication No. H10-89466, when the upshift operation is performed while the automatic upshift is executed in the manual shift mode, the shift stage display at the indicator is switched at the automatic upshift timing, rather than at the manual operation timing, and therefore the driver can be given an uncomfortable feeling.
Further, a general problem encountered when the automatic shift control is executed in the manual shift mode is that when the automatic shift control is executed, the shift stage display is switched when no shift is intended by the driver and the shift is not recognized. The resultant problem is that the driver is given an uncomfortable feeling, and this problem also remains unsolved by Japanese Patent Application Publication No. H10-89466 described above.